We have recently observed that the deleterious effect of systolic overload induced by hypertension on cardiac performance and contractile proteins in rats can be partially or completely prevented or reversed by exposing the hypertensive rats to a chronic swimming program. The purpose of the present proposal will be to further elicit the types of physical training that might protect or reverse the effects of the pathologic overload on the heart. Experiments will be conducted to determine whether physical training by running is effective; whether pre-training the animals can prevent the deleterious effect of subsequent systolic overload; and whether physical training can reverse the effects after deleterious effects of systolic overload have been well established. Several others models of pathologic overload besides renal hypertension will be investigated. These will include: Dahl hypertensive rats, spontaneous hypertensive rats, rats with mild and with severe hypertension due to coarctation of the aorta, rats with overload induced by arterial venous fistula and rats with compensatory hypertrophy associated with myocardial infarction. Additionally, myopathic hamsters will be investigated to determine the prevention or reversibility of that lesion. Experiments will include heart perfusions, studies of myocardial vascular responses, analysis of contractile protein enzymology and isoemzymes, and the role of thyroid hormones.